BMI will set good pregnancy weight gain

How much weight should a woman gain during pregnancy? Depends how much she weighs before she gets pregnant. And oh, baby, has that ever changed over the past 20 years.

According to a committee established by the National Academy of Sciences Institute of Medicine, “Women today are heavier; a greater percentage of them are entering pregnancy overweight or obese, and many are gaining too much weight during pregnancy.”

Excess weight and weight gain during pregnancy isn't just the inconvenience of bigger maternity clothes. Starting a pregnancy too heavy can set up mom and baby for serious health consequences including diabetes and heart disease.

Besides being heavier, pregnant women in America now tend to be older. And they are having more twins and triplets.

So, for the first time since 1990, the “Committee to Reexamine the Institute of Medicine Pregnancy Weight Guidelines” has established recommendations for pregnant women that match those developed by the World Health Organization. Here are the important points:

Pre-pregnancy weight – what a woman weighs before she gets pregnant – is the best determinant of how much she should gain during pregnancy. And the best way to assess pre-pregnancy weight is to calculate Body Mass Index (BMI): Weight in pounds times 703 divided by height in inches divided by height in inches again. (Or do it the easy way and go to nhlbisupport.com/bmi/ for a tool that calculates BMI.)

What about twins? Again, the guidelines vary according to mom's weight (BMI) before pregnancy. But since there is less data on twin pregnancies, the committee has set these “provisional” guidelines based on the best available data thus far: BMI 18.5-24.9, normal weight: 37-54 pounds; BMI 25.0-29.9, overweight (31-50 pounds); BMI 30 or more, obese (25-42 pounds). What about underweight women with twins? Unfortunately, not enough information is available to make a firm recommendation, these experts say.

What's the goal under these guidelines? To produce an infant who is not too small and not too large at birth. And it is remarkably clear, say the IOM experts, that women who enter pregnancy at a normal BMI (normal weight) have a better chance for producing a baby who is “just right.”